This invention relates generally to a piezoelectric oscillator semiconductor circuit and more particularly to a means for selectively adjusting the period of oscillation relative to oscillation circuits coupled to a piezoelectric oscillator.
It is known in the art to employ at least one oscillation circuit, shown in FIG. 3, in conjunction with a piezoelectric oscillator to set the oscillation frequency of the piezoelectric oscillator in the oscillator section of the combination circuit. Such an oscillation circuit comprises inverter 31, feed back resistance 32, drain resistance 33, a gate capacitance 34 connected to the gate of inverter 31 and a drain capacitance 35 connected to the drain of inverter 31. This intergrated circuit is provided with output electrode pads 38 and 39. FIG. 4 discloses the circuit of FIG. 3 in the form of semiconductor element 50 fixed on die pad 51. Element 50 is electrically connected to specified lead terminals 53, 54 and 55 via thin metal wires 52, e.g., Au wires. Piezoelectric section 56 comprising, for example, a quartz crystal oscillator is electrically connected to lead terminals 53 and 51. Then, semiconductor element 50, Au wire 52, crystal oscillator 56, die pad 51, and a part of lead terminals 53 to 55 are formed in a resin 57, such as epoxy resin or the like, by means of a transfer mold or the like as shown in FIG. 4.
In this combination of connected circuits, when the oscillation frequency of piezoelectric oscillator section 56 changes, it is also necessary to change the capacitance of the oscillation circuit in semiconductor element 50 in order to optimize stability for frequency operation at the new or changed oscillation frequency. However, the gate capacitance and the drain capacitance of the oscillation circuit, such as shown in FIG. 3, contained within semiconductor element 50 are, of course, fixed at the time of circuit fabrication. Therefore, the combination of connected circuits will oscillate under undesirable conditions so that abnormal oscillation, such as unstable oscillation, oscillation stop and the like, will occur when phase conditions, oscillation amplitude conditions or the like become unadjusted.
It is an object of the present invention to provide stable oscillation by optimizing for changes in oscillation frequency conditions even in the case when the oscillation frequency of piezoelectric oscillator is changed.